Typically, a motor takes power in the form of voltage and current. This power is converted over time into mechanical energy, for example in the form of rotation of a shaft attached to the motor to operate another device, such as a generator. Switched reluctance motors are well-known in the art. One type of reluctance motor is controlled by circuitry that determines the position of the rotor, and coil windings on the stator poles are energized as a function of rotor position. This type of reluctance motor is generally referred to as a “switched reluctance motor” or “SRM.” Rotors are typically constructed of low reluctance materials such as iron and its alloys, nickel, cobalt, etc., that tend to strongly align to an incident magnetic field. Thus, a typical SRM has a rotor with alternating regions of high and low reluctance on it, and a stator with electromagnets, that when energized in sequence, will pull the low reluctance regions, or poles of the rotor, to turn the rotor and produce power.
The number of stator poles and the number of rotor poles in a SRM may be varied resulting in many different geometries. A common geometry is a 3 phase, 4rotor, 6 stator configuration as depicted in FIG. 1, with the rotor concentric to the stator and rotably positioned relative to the stator. The stator and rotor consist of salient (projecting) poles, with wire coils wound around a portion of each stator. The field coils receive electricity from an outside source. A shaft is typically positioned centrally of the stator and rotor, coupled to the center of the rotor, to transfer the driving force of the motor to mechanical energy, for example, another device.
When current is supplied to coil windings in a motor in a magnetic field, the magnetic force produces a torque which causes the rotor to turn relative to the stator, or the stator to turn relative to the rotor, producing magnetic flux changes. An electromotive force (EMF), consistent with Faraday's law of induction, is induced in the coil windings, moving the rotor poles towards the stator poles, so as to minimize resistance. The induced EMF opposes any change, so that the input EMF that powers the motor will be opposed by the motor's self-generated EMF, called the “back” or “counter” EMF (CEMF) of the motor. The presence of CEMF will result in lower efficiency and a need for increased voltage across the coils to overcome the CEMF. If the rotor or stator is rotating slowly, the CEMF is relatively low, and a large current flows through the motor, providing a high torque. As the speed of rotation of the motor increases, the CEMF increases, reducing the current through the motor. The CEMF determines the speed of the motor for a particular voltage, such that the speed of motors is controlled by varying the supplied voltage. More torque loading will result in less speed and more current. As the load on the motor increases, the motor will slow, reducing the CEMF and permitting a larger current to flow in the coils. Because torque is proportional to current, an increase in torque results from an increase in load on the motor. By reducing CEMF, a motor can operate at significantly increased efficiencies. A motor control circuit controls the speed and torque of the motor.
Variations of a switched reluctance motor are known, for example, where permanent magnets are located between adjacent stators of a conventional switched reluctance motor. Certain of these variations are referred to as “hybrid switched reluctance motors.”
There remains a need for high torque motors that can operate at increased efficiencies to operate devices, such as DC and AC electricity generators or mechanical equipment.